A seatbelt reminder device is known that generates a warning when a seatbelt has not been attached. Among such seatbelt reminder devices are those that include a wireless seatbelt attaching detection device that detects whether or not a seatbelt is attached and wirelessly transmits the detection results. The technology described in Japanese Patent Application Laid-Open (JP-A) No. 2008-238947 has been proposed as a wireless seatbelt attaching detection device of this type.
In JP-A No. 2008-238947 there is proposed a device having a seatbelt that is placed in an attached state by firstly undergoing a preliminary operation that is performed prior to attaching and then undergoing a attaching operation, a first transmitter that wirelessly transmits a predetermined signal when the attaching operation is detected, a second transmitter that wirelessly transmits a predetermined signal when the preliminary operation is detected, a receiver that receives signals from the first transmitter and the second transmitter, and a control unit that determines the attached state of a seatbelt based on signals received by the receiver, wherein the receiver switches from an intermittent operating state to a continuous operating state as a result of receiving a signal from the second transmitter, and the control unit determines that the seatbelt is attached when the receiver receives a signal from the first transmitter after having received the signal from the second transmitter.